This application is directed toward fasteners and in particular those that are useful for selectively locking two objects to each other in a predetermined relationship.
For numerous reasons it is often useful to provide a mechanism which is able to secure or lock two objects or structures to each other in a fixed relationship and provide for a defined space between the objects. This is often desirable in electrical applications where spacing is critical in order to prevent interference between the electrical components mounted on adjacent circuit boards or between the electrical components on a circuit board and the chassis.
In the case of circuit boards, it is oftentimes necessary to mount a circuit board to a chassis. In other instances, it may be necessary to mount a series of boards in a stacked relationship. When mounting a board to a chassis the board is placed onto mounts or supports which have means for affixing the board immovably to the chassis.
Various mounts or supports in the past have been used to affix a circuit board to a chassis where a predetermined distance is intended to exist between the circuit board and the chassis. For example, a steel screw may be placed into an aperture of a circuit board with a non-conductive washer disposed between the head of the screw and the circuit board. On the other side of the circuit board from the washer a non-conductive hollow spacer is fitted over the threads of the screw. The threaded end of the screw passes through an aperture, another circuit board or a chassis and receives a second non-conductive washer and a nut. The screw and nut assembly is then tightened to secure the circuit board to the chassis or second circuit board. This screw and nut assembly is advantageous because it provides for a good mechanical fit and will not ordinarily vibrate loose. In addition, because the washers and spacer each extend a full 360.degree. about the screw, good support is provided on both sides of the circuit board or both sides of the chassis. However, there are several disadvantages associated with this type of assembly, which requires several separate pieces and multi-step installation, including high material and stocking costs and high labor cost.
Alternatively, single-piece supports exist such as those marketed by FASTEX, a division of Illinois Tool Works, Inc. These supports have one end which snaps into an aperture of a circuit board and another end which is received by an aperture in the chassis. These supports have pronged or barbed ends or are barbed at one end and have a canoe clip at the other end. These supports are advantageous because of lower product and labor installation costs. However, they do not provide for a positive mechanical fit between the ends of the support and the circuit board or chassis and as a result they can vibrate loose of the circuit board or chassis. Furthermore, the prongs or barbs offer only limited contact between the support and the circuit board which can be insufficient when certain pressure is applied to the circuit board. Lastly, these type supports are less suitable for automated installation.
It is also known that a NYLATCH fastener may be used which has an extended length grommet. The grommet is fitted through an aperture in the circuit board and a plunger is partially actuated to connect the fastener to the circuit board by partially expanding the grommet. A plurality of washers may then be fitted over a portion of the grommet that extends beyond the underside surface of the circuit card. The grommet is then placed through an aperture in a chassis and is further expanded by the plunger to secure the grommet to the chassis and thereby fasten the circuit board and chassis together with the washers acting as a spacer to maintain the circuit board and chassis a predetermined distance apart. The use of a NYLATCH fastener is advantageous because it provides for a positive mechanical fit or lock between the fastener and the circuit board or chassis. However, the NYLATCH fastener is generally secured to the circuit board before the electrical components are added to the circuit board to prevent damage thereto during installation of the fastener because of the force required to activate the plunger. Thus, the fasteners must travel with the circuit boards during production and shipping of the circuit boards which may be undesirable because, in part, larger shipping containers are required to accommodate the extending portions of the fasteners. Furthermore, the addition of the washers slows installation and results in increased product and inventory costs.